nikkismom

Hi all. I'm new here and searching for answers. My almost 20 year old grey, Nikki, seems to be going bald. She's had a small bare spot on the top of her head since I brought her home. (4 years ago) In the last couple of weeks the spot is getting bigger. She is not plucking them as she cannot reach them. The rest of her feathers are normal (beautiful as always). Can this happen with age? She is very healthy, never been sick according to her previous owner and my experience with her. Has anyone else experienced this with their greys? Any ideas? Thanks in advance, Laura